1. Field of the Invention
The present invention relates to a control circuit for a photomultiplier tube.
2. Related Background Art
A photomultiplier tube is known as a highly sensitive photodetector that detects weak light. Photoelectrons released from a photocathode in response to incidence of weak light are amplified by dynodes, collected at an anode, and outputted to the outside. However, it has been known that, when high intensity light is made incident into the photomultiplier tube, since electron multiplication exceeding a multiplication withstanding pressure of the photomultiplier tube is performed, the photomultiplier tube is broken. Conventionally, a protection circuit against such an excessive input has been provided.
In a protection circuit described in Patent Document 1 (Japanese Patent Application Laid-Open No. H03-133046), performed is control such that, when a current outputted from an anode of a photomultiplier tube exceeds a threshold for a predetermined period of time, the photomultiplier tube is powered off, judging that over-light has been made incident.
For a light shield film breakage detecting circuit described in Patent Document 2 (Japanese Patent Application Laid-Open No. 2000-121737), a light shield film is provided at the side of a light incident surface of a photomultiplier tube, and performed is control such that, when a current outputted from an anode of the photomultiplier tube exceeds a threshold, an alarm is outputted, judging that the light shield film is damaged.